It has been demonstrated that lipopolysaccharides and polysaccharides of Mycobacterium avium subsp. paratuberculosis (Mptb) are major B-cell antigens in ruminants and therefore are components of interest for the development of serological diagnostic tests. We have extracted (lipo)polysaccharides antigens from Mycobacterium bovis BCG, Mycobacterium phlei and Mptb. Electrophoresis analysis showed that the major component of this antigen preparation had an apparent MW corresponding to that described for the lipoarrabinomannan (LAM). Analysis of the reactivity of serum from animals experimentally infected with Mptb or M. bovis or sensitized to M. phlei showed strong cross-reactive responses against the LAM antigens tested even if intensity of the responses observed were greater against autologous LAM antigen. Cross-absorption studies showed that at least some epitopes seemed to be recognized by antibodies specific for the different Mycobacteria. Development of an ELISA test for the diagnostic of Mptb was performed using Mptb LAM for the plate sensitization and M. phlei LAM for the absorption step. This ELISA was evaluated on serum samples from animals originating from paratuberculosis, tuberculosis or control herds. Our results suggest: i) that the absorption step was essential for the specificity of the test; ii) and comparison with conventional commercial diagnostic tests showed at least similar performances. It was also observed that with the tests used, it was not possible to distinguish between M. bovis and Mptb infected animals.
This work was partially funded by grants from the Belgian Ministery of Agriculture (DG6).